The invention relates to the coating of elongated cylindrical bodies of a composite material, to surface dressing and finishing by means of a metal coating.
It is an object of the invention to provide a hard metallic finish on top of a non-metallic composite roll or cylinder. One example of the composite roll comprises carbon fiber composite rolls and shafts.
In this context, prior art technology comprises precision grinding of a composite roll, coating the same, for example in a vacuum, with a gas phase coating, whereafter coating can be continued electrolytically. This type of coating is used for example in the process of chromium plating plastic-bodied water faucets and the like fixtures, another example comprising chromium plated plastic automotive parts. Various metal spraying techniques have also been experimented with varying degrees of success. Although electrically conductive in itself, carbon fiber is not applicable as such to electrolytic deposition, the matrix material covering such carbon fiber being electrically non-conductive.
For example, in the process of manufacturing a precision measured paper machine roll with prior art methods, it is necessary to perform precision grinding prior to coating. The durability and service life of a coating has been a major problem. In uncoated form, however, the durability and smoothness and process engineering properties of carbon fiber and a matrix material have not always been sufficiently good.
This invention endeavors to provide a composite roll, cylinder or casing, which combines the beneficial qualities of a metal casing and, for example, a carbon fiber composite tube. A metal casing can be coated for example with hard chromium, it can be worked for a profiled surface, it can be welded, laser-engraved or engraved with more traditional methods. On the other hand, in terms of its vibration properties and weight, a composite roll is superior to a metal roll. The properties of a composite roll can be regulated by varying angles of the fibers and by varying materials for the matrix and fibers. A preferred composite roll material for a paper machine is an epoxy matrix carbon fiber roll. The inventive solution is capable of providing, for example, a composite roll for a paper machine, which is almost as light as a composite roll but has surface properties consistent with a hard-chromium plated metal roll. Of course, the same inventive solution can be used for coating other cylindrical bodies, as well. Plating a composite body with a metal, which functions as a primer or base for the ultimate coating, can be performed, as described hereinafter, either during the very process of manufacturing the composite body or applied around an already finished and dimensionally set composite roll.